1. Field of the Invention
The present invention relates to a backlight applied to a liquid crystal display unit, and particularly relates to a spread illuminating apparatus, which is preferable for a backlight of a liquid crystal display unit used for a glasses-free 3D display system.
2. Description of the Related Art
In recent years, a glasses-free 3D display system where viewers are allowed to observe three-dimensional (3D) images with no dedicated equipment such as glasses has been widely noticed. In conventional glasses-free 3D display systems, the following technologies are introduced to realize glasses-free 3D display. That is, left eye images and right eye images, which are displayed on a liquid crystal display device, are provided only toward a left eye or a right eye, respectively by controlling the light distribution of illuminating light emitted from a backlight. See Japanese Patent Application Laid-Open No. 2010-528326 (hereinafter referred to as the “Patent document”).
As illustrated in FIG. 6A, a display system 110 disclosed in the Patent document includes a liquid crystal display panel 120, a backlight 130 that supplies light to the liquid crystal display panel 120, and a double-sided prism film 140 that is arranged between the liquid crystal display panel 120 and the backlight 130. The backlight 130 includes a light guiding plate 125, a right eye image solid light source 132 arranged at a first light input face 131 of the light guiding plate 125, and a left eye image solid light source 134 arranged at a second light input face 133. Further, not illustrated, a reflection member, which returns leakage light to the light guiding plate 125, is generally arranged at a rear face 136 side of the light guiding plate 125.
The double-sided prism film 140 includes triangle prism rows facing a light output face 135 of the light guiding plate 125, the rows extending approximately in parallel to the first and second light input faces 131, 133. Further, the double-sided prism film 140 includes cylindrical lens rows facing the display panel 120, the rows also extending approximately in parallel to the first and second light input faces 131, 133. With the above structure, the directivity of light, which has been introduced from the first light input face 131 to the light guiding plate 125 and then exited out from the light output face 135, is adapted to change toward a right eye 101b of a viewer. On the other hand, the directivity of light, which has been introduced from the second light input face 133 to the light guiding plate 125 and then exited out from the light output face 135, is adapted to change toward a left eye 101a of the viewer.
In the display system 110, right eye images and left eye images are displayed alternately on the display panel 120. Here, the right eye image solid light source 132 is turned on (concurrently, the left eye image solid light source 134 is turned off) when the right eye images are to be displayed. Subsequently, the left eye image solid light source 134 is turned on (concurrently, the right eye image solid light source 132 is turned off) when the left eye images are to be displayed. In this manner, the right eye images and the left eye images are selectively provided respectively to the right eye 101b and the left eye 101a of the viewer.
The display system 110 includes a periodic driving element 150 and an image source 160 to enable the above operations.
In the glasses-free 3D display system, a so-called crosstalk has been generally known as one of the problems making complete separation between the right eye images and the left eye images failed. This crosstalk tends to occur in case that the right eye images with certain brightness are faultily supplied to the left eye of the viewer while the left eye images with certain brightness are faultily supplied to the right eye of the viewer.
For example, in the glasses-free display system of the display system 110, the following is one of the causes that such crosstalk arises. That is, partial light, which has been emitted from the right eye image solid light source 132 and then introduced into the light guiding plate 125 through the first light input face 131, arrives to the second light input face 133 without being emitted out from the light output face 135. The partial light is then reflected at the second light input face 133, and emitted from the light output face 135. The reflected light will then direct toward the left eye 101a of the viewer. The same can be said about light that has been emitted from the left eye image solid light source 134 and introduced into the light guiding plate 125 through the second light input face 133.
In the Patent document, as illustrated FIG. 6B, a reflection preventing mechanism 137 is formed on the second light input face 133. Light that has been emitted from the right eye image solid light source 132 and then introduced into the light guiding plate 125 through the first light input face 131 can be prevented from reflecting at the second light input face, contributing to the reduction of crosstalk. Here, light that has been emitted from the left eye image solid light source 134 is introduced into the light guiding plate 125 by passing through each input opening 138 at which the reflection preventing mechanism 137 is not formed. The same reflection preventing mechanism and input opening are also formed at the first light input face 131.